Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $218.93   11.727%   $244.6039   $244.60   $244.60   $244.60  
  Purchase #2 $159.33   3.732%   $165.2762   $165.28   $165.30   $165.30  
  Purchase #3 $149.81   7.561%   $161.1371   $161.14   $161.15   $161.10  
  Purchase #4 $179.88   8.811%   $195.7292   $195.73   $195.75   $195.70  
  Purchase #5 $214.40   3.764%   $222.47   $222.47   $222.45   $222.50  
  Purchase #6 $73.63   12.260%   $82.657   $82.66   $82.65   $82.70  
  Purchase #7 $38.26   7.188%   $41.0101   $41.01   $41.00   $41.00  
  7 purchase totals = $1,034.24       $1,112.8835   $1,112.89   $1,112.90   $1,112.90